Liquid crystal display apparatuses are requested to provide uniform display indication. Further, in order to moderate individual differences among multiple display apparatuses at the time of being used in a multi-monitor mode, liquid crystal display apparatuses are demanded to provide uniform display quality such that the liquid crystal display apparatuses can exhibit fixed luminance and white balance, and exhibit no luminance unevenness (no ununiformity of luminance within a backlight surface thereof) and no color unevenness (no ununiformity of chromaticity within a backlight surface thereof). However, in a liquid crystal display apparatus, changes of luminance and white balance, luminance unevenness (ununiformity of luminance within the backlight surface) and color unevenness (ununiformity of chromaticity within the backlight surface) can be caused by various factors, such as distribution of luminance and color coming from the structure of its backlight source; distribution of transmittance and color coming from production variations in pixels of its liquid crystal panel; and individual variations and an aging change of its light source components.
In view of that, the following proposal has been made to provide an improvement to reduce luminance unevenness (ununiformity of luminance within the backlight surface), color unevenness (ununiformity of chromaticity within the backlight surface), and a change in white balance in a display region of a liquid crystal display apparatus. That is, there is provided a liquid crystal display apparatus in which LEDs with single color or different colors are used for its backlight source, and a light emitting region of the backlight source is divided into multiple regions. The divided multiple regions are controlled individually so as to achieve the above-described improvement.
Further, LEDs to be used as a light source greatly change in light emitting state depending on an aging change and a temperature condition. In view of that, another proposal has been made in order to maintain the uniform display indication. That is, there is provided a liquid crystal display apparatus employing color sensors, and the backlight source of the liquid crystal display apparatus includes LEDs disposed in multiple regions. The color sensors measure light emitted by LEDs in the multiple regions of the backlight source, and light emission of the LEDs in each of the multiple regions is corrected in accordance with the measurement values.
In liquid crystal display apparatuses having such a constitution that color sensors measure light emission of LEDs, a color sensor which can measure light quantities of RGB color components of received light by using color filters is mainly used, rather than a color sensor which can measure the chromaticity of received light, which is specified by the degree of human subjectivity, such as coordinates of the XYZ color space. LEDs are changed due to temperature not only in an amount of light emission, but also in emission spectrum. The change of LEDs in emission spectrum affects measurement values of the color sensor.
Further, also a color sensor itself is affected by temperature. Therefore, it is difficult to properly maintain the luminance and white balance of a display screen of a liquid crystal display apparatus. Accordingly, a proposal has been made so as to use a temperature sensor for measuring a temperature in order to correct the measurement values of the color sensors.
FIG. 24 illustrates a constitution of a conventional liquid crystal display apparatus described in Japanese Unexamined Patent Application Publication (JP-A) No. 2006-276784. As illustrated in FIG. 24, the liquid crystal display apparatus disclosed in JP-A No. 2006-276784 is equipped with a backlight, and includes light emitting diodes (LEDs) with three colors of red, green, and blue, a color sensor disposed with corresponding to the light emitting diodes, and a temperature sensor to measure the temperature of the light emitting diodes. The liquid crystal display apparatus further includes a control computing unit configured to correct two types of chromaticity change of the light emitting diodes, where one is a chromaticity change caused by the temperature of the light emitting diodes and the other is a chromaticity change which occurs at the time of adjusting the brightness of the red, green and blue light emitting diodes. Such a constitution reduces the chromaticity change of the light emitting diodes coming from the used environment and maintains an arbitral luminance and chromaticity of the backlight.
This constitution makes possible to correct the luminance and color of the whole display screen collectively in accordance with the temperature of the whole backlight, which can reduce changes in the luminance and the white balance of the whole screen.
However, in this constitution, the light emitting region of the backlight is not divided. Accordingly, this constitution does not adjust the luminance unevenness (ununiformity of luminance within the backlight surface) and the color unevenness (ununiformity of chromaticity within the backlight surface) inside of the backlight. Further, the backlight is provided with only one color sensor. When temperature distribution takes place at the inside of the backlight, the light emitting state of each LED at a different position in the backlight changes due to the temperature of the corresponding portion inside of the backlight, and the color sensor detects just the sum of light emitted by the LEDs in such various light emitting states. As a result, the above constitution has a problem that luminance unevenness (ununiformity of luminance within the backlight surface) and color unevenness (ununiformity of chromaticity within the backlight surface) take place. Furthermore, the backlight is provided with only one temperature sensor. Such a temperature sensor does not measure the temperature distribution inside of the backlight directly, and does not measure temperature distribution caused inside of the backlight due to self-heat generation of the LEDs in the backlight, separately from the temperature change of the whole backlight due to the ambient temperature. Therefore, the temperature distribution inside of the backlight is not estimated. Accordingly, the above constitution still has a problem that luminance unevenness (ununiformity of luminance within the backlight surface) and color unevenness (ununiformity of chromaticity within the backlight surface) take place on the display screen.
FIG. 25 illustrates a constitution of a conventional liquid crystal display apparatus described in JP-A No. 2008-249780. As illustrated in FIG. 25, the liquid crystal display apparatus in JP-A No. 2008-249780 includes a liquid crystal panel and a backlight panel which lights the liquid crystal panel from its back surface, and is configured to perform display based on image data. The liquid crystal display apparatus further includes a region luminance calculating unit (light adjustment controller), backlight luminance sensors, a controller and an LED driver, and is constituted as follows. The liquid crystal panel is divided into multiple display regions, and the region luminance calculating unit is configured to calculate the luminance of each of the multiple display regions on the basis of the image data. On the backlight panel, multiple backlight regions (backlight sections) are defined. The backlight luminance sensors are disposed in the multiple backlight regions, respectively, and each backlight luminance sensor is adapted to measure luminance of light emitted by the corresponding backlight regions. The controller is configured to adjust the luminance of each of the multiple backlight regions on the basis of the luminance of the corresponding display region and the luminance of light emitted by the corresponding backlight region. The LED driver is configured to drive LEDs (white LED element) of the backlight panel. Further, the backlight luminance sensor is made to include a temperature sensor and a light sensor.
Since this constitution is configured to separately adjust the luminance of each of the multiple backlight regions defined on the backlight panel, the luminance unevenness (ununiformity of luminance within the backlight surface) and color unevenness (ununiformity of chromaticity within the backlight surface) in the display screen can be corrected with the constitution, by adjusting the luminance of each region of the backlight properly. Further, since the backlight luminance sensor disposed in each of the backlight regions includes a temperature sensor and a light sensor, in the case where temperature distribution occurs inside of the backlight, it is possible for the backlight luminance sensor to measure directly the temperature distribution as far as the backlight regions are defined densely in comparison with the change of the occurring temperature distribution. Accordingly, even if a temperature distribution occurs inside of the backlight, it becomes possible to correct the luminance unevenness (ununiformity of luminance within the backlight surface) and the color unevenness (ununiformity of chromaticity within the backlight surface) caused on the screen due to the temperature distribution.
However, such constitution needs establishment of a large number of backlight regions so as to become sufficiently dense in comparison with the luminance unevenness (ununiformity of luminance within the backlight surface) and color unevenness (ununiformity of chromaticity within the backlight surface) which occur in the backlight, and with a temperature distribution which occurs inside of the backlight. It further needs a temperature sensor and an expensive light sensor to be disposed in each of a large number of regions. This constitution has a problem that the cost of such components increases greatly. Further, since the controller to adjust the luminance of each of the backlight regions, has an increased number of pins in order to communicate with a number of sensors, the circuit size of the controller becomes larger. Furthermore, an increase of the number of measurement parameters complicates computing processing of the controller, and needs the controller to have higher computing processing capability. Such condition also arises a problem that the cost increases.
FIG. 26 illustrates a constitution of a conventional lighting apparatus disclosed in JP-A No. 2007-317479. As illustrated in FIG. 26, the lighting apparatus disclosed in JP-A No. 2007-317479 includes a first light emitting region, a second light emitting region, a first photo-detector, a second photo-detector, and a light source controller, and is configured as follows. On the first light emitting region, a plurality of first light sources are disposed, and on the second light emitting region, a plurality of second light sources are disposed. When multiple light sources are in a lighting state, the first light emitting region becomes relatively high temperature, and the second light emitting region becomes relatively low temperature. The first photo-detector is adapted to receive mainly light emitted from the first light sources, and the second photo-detector is adapted to receive mainly light emitted from the second light sources. The light source controller is configured to control the plurality of first light sources collectively on the basis of the output of the first photo-detector and to control the plurality of second light sources collectively on the basis of the output of the second photo-detector.
According to this constitution, the light emitting regions are classified into the first light emitting region which becomes relatively high temperature and a second light emitting region which becomes relatively low temperature. The photo-detector is disposed for each kind of the light emitting regions, and each kind of the light emitting regions is controlled collectively on the basis of the output of the corresponding one of the photo-detectors. Accordingly, by conducting luminance adjustment for each kind of the light emitting regions, the constitution makes possible to correct the luminance unevenness (ununiformity of luminance within the light guide plate) and the color unevenness (ununiformity of chromaticity within the light guide plate) of the lighting apparatus. Further, even when temperature distribution occurs inside of the lighting apparatus, such constitution indirectly measures the light quantity of the high temperature region and the light quantity of the low temperature region without measuring directly the temperature distribution. Accordingly, by correcting a change of light sources caused due to the occurring temperature distribution, such constitution can reduce the luminance unevenness (ununiformity of luminance within the light guide plate) and the color unevenness (ununiformity of chromaticity within the light guide plate) of the lighting apparatus caused due to the temperature distribution as far as the temperature is distributed inside of the lighting apparatus one-dimensionally and the high temperature portions and the low temperature portions appear line-symmetrically in the lighting apparatus.
However, when the temperature is distributed inside of the lighting apparatus two-dimensionally, such lighting apparatus needs a large number of regions defined so as to become sufficiently dense in comparison with the temperature distribution occurring inside of the backlight. It means that the lighting apparatus further needs an expensive optical sensor for each of the large number of regions, and the above constitution has a problem that the cost of such components increases greatly. Furthermore, most of color sensors are generally configured to measure light quantities of RGB color components of received light by using color filters, rather than to measure the chromaticity of received light, which is specified by the degree of human subjectivity, such as coordinates of the XYZ color space. LEDs are changed due to temperature not only in an amount of light emission, but also in emission spectrum. The change of LEDs in emission spectrum affects measured values of the color sensor. Further, also a color sensor itself is affected by temperature. Therefore, it is difficult for the lighting apparatus without employing a temperature sensor to properly maintain the luminance and white balance. Furthermore, in the case where the luminance of LEDs deteriorates due to the use for long term, it becomes necessary to operate the LEDs with greater power. However, in such a situation, as compared with the initial stage of the product, the temperature change at the inside of the lighting apparatus becomes larger, and the above-described influence of the change of the LEDs in light emission spectrum onto the color sensor further increases. Accordingly, it becomes more difficult for such lighting apparatus to maintain the luminance and the white balance, which is a problem.
FIG. 27 illustrates a constitution of a conventional liquid crystal display apparatus disclosed in JP-A No. 2006-126627. As illustrated in FIG. 27, the liquid crystal display apparatus disclosed in JP-A No. 2006-126627 has the following constitution. A liquid crystal display panel, which includes multiple display pixels, is attached to a housing and is configured to display images on the basis of image signals. The liquid crystal display apparatus includes an internal temperature sensor to measure the back surface temperature of the liquid crystal display panel, and a temperature sensor to measure a temperature outside of the housing. A control section stores to a ROM (Read Only Memory), data to be used for estimation of a temperature on a display surface of the liquid crystal display panel based on the respective temperatures measured by the both sensors, where the data is in the form of a table. At the time of actuating an ODC (Over Drive Control) circuit, the control section operates the ODC circuit to read the data from the ROM on the basis of the temperatures measured by the both sensors, and to adjust an overshoot voltage and an undershoot voltage of the ODC circuit.
If there is provided a liquid crystal display apparatus in which only an internal temperature sensor measures the temperature of the liquid crystal display panel and the overshoot voltage and the undershoot voltage are determined by using the measured temperature, the following problems may arise. With such construction, a rapid change of the outside air temperature can cause the construction to erroneously determine the temperature of the liquid crystal display panel, the ODC circuit may use an erroneous overshoot voltage and undershoot voltage, and then, the function of the ODC circuit is not sufficiently exhibited, which may prevent reduction of the blur (unclearness) of a displayed image. Further, such situation may make the condition that the voltage of a pixel electrode becomes a state of exceeding a target transmittance and the corresponding pixel may show erroneous color. JP-A No. 2006-126627 describes that the disclosed constitution can solve all of these problems.
However, the technology disclosed in JP-A No. 2006-126627 relates to an overshoot drive of the liquid crystal display apparatus, in which the temperature of the liquid crystal panel in contact with the outside air is corrected. The disclosed technique is to estimate the temperature of a liquid crystal panel on the basis of an outside air temperature which greatly changes depending on the surrounding environment and of a temperature measured with an inner temperature sensor at a position distant from the liquid crystal panel, in place of measuring the temperature of the liquid crystal panel surface directly. For this reason, if the apparatus does not determine an amount of the correction properly for all the possible situations caused by the outside air temperature which can rapidly change depending on the surrounding environment and on a working condition, a problem remains in that the apparatus hardly performs an accurate correction. In JP-A No. 2006-126627, there is a description about the temperature correction using a panel representative value, but there is no description about a temperature distribution at the inside of the backlight. That is, the document does not describe about a problem that luminance unevenness (ununiformity of luminance within the backlight surface) and color unevenness (ununiformity of chromaticity within the backlight surface) occur on the display screen.
The present invention seeks to solve the problems.